Download Well Disinfection Procedure

SAN LUIS OBISPO COUNTY ENVIRONMENTAL HEALTH SERVICES
DISINFECTION OF PRIVATE WATER WELLS
This handout has been prepared to tell owners of private wells how to disinfect a well that has had an
unsatisfactory laboratory water report and to answer questions concerning water supplies that are
often asked of the county health department.
A laboratory analysis alone will not show whether or not water is safe for human consumption. So far
as ill health from water is concerned, the principal danger is intestinal disease from contamination of
water by human sewage. Total coliform bacteria are an indicator of the sanitary condition of a water
supply. The presence of coliform bacteria in a water supply shows possible pollution that may
contain disease causing organisms. Total coliform bacteria are found in soil, in water that is on or
near the surface of the ground, and in human and animal wastes. The total coliform group can
survive longer in water than most disease causing organisms and are easier to identify. Therefore,
safe water contains no total coliform bacteria.
When total coliform bacteria are found in a private well supply, the first step is usually to check the
well for any physical defects. A broken or missing well cap, or a well casing that is too close to the
surface of the ground or is located beneath the ground, can allow surface water, insects, and debris
to enter the well. These conditions should be corrected and then the water should be retested.
If your well requires disinfection, use the following procedure:
1. Inform all users of the water that it will not be fit for use for 8-12 hours or longer.
2. Add to the well one-gallon or more of household bleach such as Clorox, Purex, etc., mixed with 35 gallons of water, making an attempt to wash down the inside of the casing and the surface of the
drop pipe.
3. Allow to stand 30 minutes so the chlorine can settle. Then start and stop the pump repeatedly to
mix the water and chlorine.
4. Let stand one hour and repeat pumping as under (3).
5. Open all taps until chlorine is smelled, tasted or tested in the water. Then close the taps and allow
to stand overnight (or 8-12 hours). Disconnect or bypass any activated carbon filter system.
6. Flush out the system beginning with the well. Use a hose connected to an outside hose bibb and
run until the odor of chlorine is gone or the chlorine test is negative. Do not discharge to a septic
system or lawn. After the water from the well is free from chlorine, flush the remainder of the
piping system.
7. Take all necessary steps to completely seal the well from any further contamination.
8. Contact the San Luis Obispo County Public Health Department, Environmental Health Services, at
781-5544 if you additional questions.
L \Clencal\Forms\BACKSIDE BACTERIOLOGICAL - Disinfection of Well doc February 25, 2011